What is your computer system and Firefox?

Please try this; Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox.

After it is fully loaded, close it. Is the problem still there?

FredMcD said

What is your computer system and Firefox? Please try this; Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. After it is fully loaded, close it. Is the problem still there?

My computer system is Windows 8, my Firefox version is 36.0.1.

I have fully uninstalled Firefox , deleted my profile and installed an older version (34.0.5). Later I updated my Firefox to the latest version, that problem didn't happen again. Although the problem seems to be solved, I am still confused that when I removed my Firefox and installed the latest version, the problem still there.

It's possible a corrupt file caused the issue, and was removed.

FredMcD said

It's possible a corrupt file caused the issue, and was removed.

I am not sure what's happening. That problem occurred again after I updating my Firefox from 34.0.5 to the latest version, so I have to downgrade to the older version.

This is not a cure but will make it easier if Firefox locks up in Windows. https://support.mozilla.org/questions/997866 {web link}

http://kb.mozillazine.org/Firefox.exe_always_open

https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding

starrybird said

I am running Firefox 36.0.1 on Windows 8. I have had the issue since tomorrow that, if I exit Firefox and later want to start it up again, I get an error dialog that its already running. Trying to stop the process with Task Manager results in an error indicating that the process cannot be closed due to access rights. The only way to clear this is to reboot, which is so frustrating. The problem happens every time when I use Firefox. I have download an older version (34.0.5), that problem didn't happen again. Anyone else have this problem?

Same here, on W7pro. and the buttons (_ full x) disappeared...) so I went back to v. 35. for now... I surmise the changes in Flash brought this on, as I have to use IE to play news, and I no longer get the never-ending commercials. That is a bonus!

wdhc said

Same here, on W7pro. and the buttons (_ full x) disappeared

If you have problems with current Shockwave Flash plugin versions then check this:

• see if there are updates for your graphics drive drivers

https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)

https://forums.adobe.com/message/4468493#TemporaryWorkaround

• disable hardware acceleration in the Flash plugin

https://forums.adobe.com/thread/891337 See also:

• http://kb.mozillazine.org/Flash#Troubleshooting